commit db55262f8159332da4f99d3b8a10bce1c341f18d
Author: Erez Zadok <[EMAIL PROTECTED]>
Date: Wed Oct 31 20:33:46 2007 -0400
Unionfs: avoid a deadlock during branch-management on a pivot_root'ed union
Signed-off-by: Erez Zadok <[EMAIL PROTECTED]>
diff --git a/fs/unionfs/union.h b/fs/unionfs/union.h
index 659d6cc..b1fef7d 100644
--- a/fs/unionfs/union.h
+++ b/fs/unionfs/union.h
@@ -142,15 +142,22 @@ struct unionfs_sb_info {
* This rwsem is used to make sure that a branch management
* operation...
* 1) will not begin before all currently in-flight operations
- * complete
+ * complete.
* 2) any new operations do not execute until the currently
- * running branch management operation completes
+ * running branch management operation completes.
+ *
+ * The write_lock_owner records the PID of the task which grabbed
+ * the rw_sem for writing. If the same task also tries to grab the
+ * read lock, we allow it. This prevents a self-deadlock when
+ * branch-management is used on a pivot_root'ed union, because we
+ * have to ->lookup paths which belong to the same union.
*/
#ifdef CONFIG_PREEMPT_RT
struct compat_rw_semaphore rwsem;
#else /* not CONFIG_PREEMPT_RT */
struct rw_semaphore rwsem;
#endif /* not CONFIG_PREEMPT_RT */
+ pid_t write_lock_owner; /* PID of rw_sem owner (write lock) */
int high_branch_id; /* last unique branch ID given */
struct unionfs_data *data;
};
@@ -238,10 +245,30 @@ static inline off_t rdstate2offset(struct
unionfs_dir_state *buf)
return tmp;
}
-#define unionfs_read_lock(sb) down_read(&UNIONFS_SB(sb)->rwsem)
-#define unionfs_read_unlock(sb) up_read(&UNIONFS_SB(sb)->rwsem)
-#define unionfs_write_lock(sb) down_write(&UNIONFS_SB(sb)->rwsem)
-#define unionfs_write_unlock(sb) up_write(&UNIONFS_SB(sb)->rwsem)
+static inline void unionfs_read_lock(struct super_block *sb)
+{
+ if (UNIONFS_SB(sb)->write_lock_owner &&
+ UNIONFS_SB(sb)->write_lock_owner == current->pid)
+ return;
+ down_read(&UNIONFS_SB(sb)->rwsem);
+}
+static inline void unionfs_read_unlock(struct super_block *sb)
+{
+ if (UNIONFS_SB(sb)->write_lock_owner &&
+ UNIONFS_SB(sb)->write_lock_owner == current->pid)
+ return;
+ up_read(&UNIONFS_SB(sb)->rwsem);
+}
+static inline void unionfs_write_lock(struct super_block *sb)
+{
+ down_write(&UNIONFS_SB(sb)->rwsem);
+ UNIONFS_SB(sb)->write_lock_owner = current->pid;
+}
+static inline void unionfs_write_unlock(struct super_block *sb)
+{
+ up_write(&UNIONFS_SB(sb)->rwsem);
+ UNIONFS_SB(sb)->write_lock_owner = 0;
+}
static inline void unionfs_double_lock_dentry(struct dentry *d1,
struct dentry *d2)
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